This invention relates to an electromagnetic valve best suited for spilling a high-pressure fluid and to a unit fuel injector incorporating such an electromagnetic valve.
U.S. Pat. Nos. 4,392,612, 4,463,900, 4,470,545, 4,485,969, 4,527,737 and 4,618,095 disclose unit fuel injectors for injecting fuel into an engine such as a diesel engine. Such a unit fuel injector comprises a pump mechanism, an injection nozzle mechanism, and an electromagnetic valve all of which are incorporated in a body of the fuel injector, the unit fuel injector being mounted directly on the engine.
The pump mechanism includes a plunger received in a hole in the injector body so as to reciprocally move therealong, and a pump chamber whose volume is changed with the reciprocal movement of the plunger.
The injection nozzle mechanism includes injection ports communicating with the pump chamber via a fuel feed passage, and a valve disposed between the pump and the injection ports. When the pressure of fuel within the pump chamber increases to a high level during the advance or pump stroke of the plunger which decreases the volume of the pump chamber, the valve is opened to inject the fuel from the injection ports.
The electromagnetic valve controls the relief of the fuel pressure within the pump chamber during the pump stroke of the plunger so as to control the timing of terminating the fuel injection and, if necessary, the timing of starting the fuel injection. The electromagnetic valve includes a guide hole and a spill chamber both of which are formed in the injector body and communicate with each other. A valve seat is formed on one end surface of the guide hole facing the spill chamber. The electromagnetic valve also includes a poppet-type valve member which has a stem portion and a head formed at one end of the stem portion, the head being greater in diameter than the stem portion. The stem portion has an annular recess formed in its outer peripheral surface and disposed adjacent to the head. The stem portion is received in the guide hole for sliding movement therealong, so that an annular space is formed between the annular recess and the inner peripheral surface of the guide hole. This annular space communicates with the pump chamber via a spill passage formed in the injector body. The head of the valve member is disposed in the spill chamber, and is brought into and out of contact with the valve seat. The electromagnetic valve further includes an electromagnetic drive means for controlling the movement of the valve member. The electromagnetic drive means comprises an armature connected to the other end of the stem portion of the valve member, a solenoid for driving the armature so that the head of the valve member can be moved toward the valve seat, and a spring urging said valve member away from the valve seat.
In the above conventional unit fuel injector, when the solenoid is energized during the pump stroke of the plunger, the head of the valve member is brought into engagement with the valve seat, so that the communication of the spill chamber with the pump chamber is interrupted. As a result, the fuel within the pump chamber is pressurized and is injected from the injection nozzle mechanism.
When the solenoid is switched from its energized condition to its de-energized condition during the pump stroke of the plunger, the head of the valve member is brought out of contact with the valve seat under the influence of the spring. As a result, the high-pressure fuel within the pump chamber is spilled into the spill chamber, so that the pressure within the pump chamber decreases, thereby terminating the fuel injection.
When the head of the valve member is kept in sealing engagement with the valve seat, the pressure within the annular recess of the valve member is uniform, and besides the pressure receiving areas of the opposed side surfaces of the annular recess are equal to each other, so that the force due to the fuel pressure will not serve to move the valve member. However, at the moment when the head of the valve member is disengaged from the valve seat, the annular recess is communicated with the sill chamber, so that the fuel pressure within the annular recess becomes lower progressively toward the valve seat. In other words, the pressure acting on the side surface of the annular recess close to the valve seat is lower than the pressure acting on the other side surface remote from the valve seat. Because of this pressure difference, there develops a force to move the valve member in such a direction that the head of the valve member is moved toward the valve seat. Therefore, the speed of disengagement of the head from the valve seat becomes lower, so that the area of flow between the valve seat and the valve member can not be increased quickly. This retards a pressure drop in the pump chamber. As a result, the fuel injection operation can not be terminated at a time, and the problem of subsequent dripping of the fuel can not be positively overcome.
In the unit fuel injector disclosed in the aforesaid U.S. Pat. No. 4,470,545, a flange is formed on the valve member, and this flange receives the kinetic energy of the spilled fuel when the valve member is moved in its opening direction. Further, in a unit fuel injector disclosed in U.S. patent application Ser. No. 395,432 filed Aug. 17, 1989 by the Applicant of the present application, a flange is formed on a valve member, and the pressure of the spilled fuel is applied to the flange when the valve member is moved in its opening direction, and the force due to this fuel pressure serves to move the valve member in its opening direction. Further, in a unit fuel injector disclosed in U.S. patent application Ser. No. 390,893 filed Aug. 8, 1989 by the Applicant of the present application, means is provided for communicating a spill chamber with a tank of a low pressure.
The unit fuel injectors of the aforesaid U. S. patents suffer from another problem. More specifically, the injector body has a first portion extending vertically, and a second portion extending laterally from the upper section of the first portion. The pump mechanism is mounted on the upper end section of the first portion, and the injection nozzle mechanism is mounted on the lower end section of the first portion. The electromagnetic valve is mounted on the second portion. In such a construction, since the second portion of the injector body is projected laterally, the injector body occupies much space in the vicinity of the engine, and therefore reduces the space used for mounting other parts.
As is clear from the foregoing description, when the fuel pressure within the pump chamber increases, the fuel pressure within the long spill passage connected between the electromagnetic valve and the pump chamber, as well as the fuel pressure within the fuel feed passage connected between the pump chamber and the injection ports, increases. Therefore, the spill passage constitutes a dead space when the fuel is pressurized, and thus prevents the fuel from being pressurized to a sufficiently high level. Another problem is that considerable time and labor are required to form such a spill passage in the injector body, which increases the manufacturing cost.
Further, in unit fuel injectors disclosed in U.S. Pat. Nos. 4,622,942 and 4,674,461, a pump mechanism is mounted on an upper end portion of a body, and an injection nozzle mechanism is mounted on a lower end portion of the body, and an electromagnetic valve is mounted on a portion extending laterally from the body intermediate the opposite ends of the body. This unit fuel injector also suffers from the same drawbacks as described for the above-mentioned unit fuel injectors.
Further, in a unit fuel injector disclosed in Japanese Laid-Open Utility Model Application No. 115589/87, an electromagnetic valve, a pump mechanism and an injection nozzle mechanism are mounted on a vertically-extending body and disposed on the axis of the body. However, this conventional unit fuel injector differs from the unit fuel injectors of the present invention in that the electromagnetic valve is mounted on the upper end of the body, with the pump mechanism disposed between the electromagnetic valve and the injection nozzle mechanism, and that a plunger of the pump mechanism is disposed perpendicular to the axis of the body, so that during the reciprocal movement of the plunger, the body is subjected to vibrations in the direction perpendicular to the axis of the body.